An essential part of I/O design is to limit the interface noise, ground bounce and cross-talk. This has become increasingly important as the pin count for complex ICs has increased.
One approach to reducing power/ground noise has been to add more power and ground pins. Another solution has been to include a decoupling capacitor between power and ground and yet another has been to control the slew rate of the driver output, to make the turn-on more gradual by providing several driver legs, each designed with a different turn-on time and turn-on rate.
Yet another approach to reducing I/O noise is described in commonly owned application, previously filed, entitled “HIGH SPEED LOW NOISE I/O DRIVER WITH FEEDBACK CONTROL”. In this I/O driver the slew rate is controlled by providing at least one conventional I/O leg comprising a predriver and an output driver, and providing at least one secondary leg comprising a predriver and an output driver, wherein the secondary leg is controlled by feedback from the output of the I/O driver.
The present invention provides another approach to reducing the slew rate of the I/O driver by also making use of feedback from the I/O driver output.